1. Field of the Invention
The present invention relates to a melt extrusion processes, and more particularly relates to melt extrusion processes for making polypropylene fibers or films.
2. Background of the Invention
Processes for making polymeric fibers and films are known, see U.S. Patent Nos. Knox, U.S. Pat. No. 4,156,071, issued May 22, 1979, Frankfort et al, U.S. Pat. No. 4,134,882, issued Jan. 16, 1979, Piazza et al., U.S. Pat. No. 3,772,872, issued Nov. 20, 1973, Petrille, et al., U.S. Pat. No. 3,771,307, issued Nov. 13, 1973, Kilian, U.S. Pat. No. 3,002,804, issued Oct. 3, 1961, Coates et al., U.S. Pat. No. 2,957,747, issued Oct. 25, 1960, Hebeler, U.S. Pat. No. 2,604,667, issued Jul. 29, 1952, all of which are incorporated herein by reference, and Great Britain Patent Nos. 903427, published Aug. 15, 1962, 1487843, published Oct. 5, 1977 and 1574305, published Sep. 3, 1986, all of which are incorporated herein by reference. Phosphites are known stabilization additives for polyolefins, see York, U.S. Pat. No. 4,305,866, Lewis, U.S. Pat. No. 4,403,053, issued Sep. 6, 1983 and Valdiserri et al, U.S. Pat. No. 4,302,383, issued Nov. 24, 1981, all of which are incorporated herein by reference.
Polyolefin processors are attempting to process polymer at increasing temperatures and with increased shear and work on the polymer. They are also processing polymer which may contain polymerization catalyst residues. The total residual metal content has been decreasing in recent years but the catalyst residue may still be active.
This combination of more abusive processing conditions and the possibility of catalyst residue still being active may lead to difficulties when trying to process the polymers.
Catalyst "neutralizers" are well known in the art and are generally used in most formulations to inhibit corrosion of processing equipment resulting from catalyst residues. Typical examples would be: Ca, Zn, or Mg Stearates, Ca, Zn, or Mg oxides and synthetic hydroltalcite compositions such as a product manufactured and sold by Kyowa as DHT4A. Additionally products such as the Calcium Stearoyl Lactates and Calcium Lactates have been shown to be beneficial in catalyst neutralization as evidenced by reduced corrosion.
In many of the high temperature melt processes such as fiber spinning and film manufacture, screen packs are utilized to remove small particles which may be in the polymer prior to the polymer passing through the small orifices used in fiber and film processes. With the higher processing temperature/high shear applications there is a tendency for some combinations of polymers and additive formulations to be prone to screen pack plugging.
Specifically, it has been discovered, however, that stabilized polyolefin compositions containing residual catalysts, can generate solid byproducts during melt extrusion processes. These solids must be filtered out from the melt stream.
For example, melt stream fiber forming processes and film forming processes or the fiber and/or film forming dies will become clogged or the final articles (films/fibers) will exhibit defects and blemishes. Too much solid generation will lead to frequent filter clogging, referred to as screen pack plugging, which leads to increased processing pressures and reduced process throughput.
Consequently, there is a need for improved polyolefin compositions and improved melt extrusion processes that will exhibit reduced solid byproduct formation and a resulting reduced filter clogging and a reduced increase in processing pressure and improve in throughputs.